The present invention is generally related to geotechnical systems and structure elements and, more particularly, is related to an apparatus and method for in situ measurement of the relationship between interface strength and surface roughness of civil engineering construction materials for the purpose of establishing friction parameters and characteristics.
In geotechnical engineering, one of the most important factors for consideration when designing geotechnical systems is the particulate-continuum interface. This interface occurs between the soil and the geotechnical structural members (e.g. soil-concrete, soil-steel, soil-geomembrane). Although a significant amount of research has been performed on the behavior of soil masses under typical loading and straining conditions in geotechnical systems, the region where the geotechnical structural members and soil masses come into contactxe2x80x94the soil-geomaterial interfacexe2x80x94has received markedly less attention.
The interface is the primary factor governing the performance of many geotechnical systems, including for example deep foundations, micro-tunneling, liner systems (e.g. landfills, canal liners, leach ponds), and an assortment of retaining structures such as anchored, reinforced, and soil nailed walls. The importance of the characteristics and behavior of the interface between man-made geomaterials and soils in the overall system performance varies from application to application, but is usually reflected in some manner in the design methodology and associated calculations for each geotechnical system. Because the structural integrity of many systems is dependant upon accurate calculations and designs for the soil-geomaterial interface, correctly measuring, calculating and designing the performance characteristics of the interface is crucial.
There are many different types of penetrating probes for detecting and measuring soil properties and characteristics or for detecting and measuring the properties and characteristics of underground substances, such as water, gases, contaminants, etc. Probes that test for underground substances are often used primarily in association with environmental applications. For instance, U.S. Pat. Nos. 6,208,940 and 6,236,941 both to Kram describe a piezocone having a conical tip attached to the lower end of a smooth friction sleeve, where the sleeve measures the resistance of the soil. The Kram inventions use the piezocone to develop hydrostatic and hydraulic plots for detecting the depth of subsurface water and groundwater contamination.
In U.S. Pat. No. 5,663,649 to Topp, a soil penetrometer and method are disclosed which are capable of determining the soil moisture content via in situ measurements and simplified calculations. The penetrometer has a releasably engageable tip and utilizes an electromagnetic field to detect moisture. Other prior art utilizes a variety of techniques in combination with penetrometers to detect and measure in situ characteristics, such as chemical composition for identification of contamination. For instance, U.S. Pat. No. 6,097,785 to Elam discloses the use of a penetrometer equipped with x-ray fluorescence spectroscopy to identify hazardous waste; U.S. Pat. No. 6,147,754 to Theriault uses laser induced breakdown spectroscopy in conjunction with a penetrometer to identify soil contamination; U.S. Pat. No. 6,018,389 to Kyle uses fiber optic raman spectroscopy probes to provide in situ chemical analysis; and U.S. Pat. No. 5,497,091 to Bratton teaches the use of cone penetration testing (CPT) in conjunction with a surface-mounted pH sensor to provide continuous pH profiling with depth during penetration.
It is also known in subsurface testing systems to utilize cone and sleeve strain sensors to detect certain soil characteristics. In U.S. Pat. No. 5,635,710 to Reed, a detachable sleeve is used to provide strength and protection to the radiation sensor probes which detect subsurface formations, and U.S. Pat. No. 5,902,939 to Ballard discloses a penetrometer having cone and sleeve strain sensors used to calculate soil classifications and soil layers in xe2x80x9creal-timexe2x80x9d during penetration. Likewise, in U.S. Pat. No. 5,726,349 to Palmertree, a system and method for determining the shear resistance of soil with a portable and partially automated cone penetrometer is provided, where the field data outputs are stored and then transferred to a computer for tabulating.
Clearly, the ability to accurately measure and anticipate the behavior of soil-geomaterial interfaces does not exist and development of such a system would lead to more accurate and reliable prediction of interface strength and more efficient geotechnical structure designs.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
Briefly described, one embodiment of the system, among others, can be implemented as follows. A multi-friction sleeve penetrometer attachment apparatus that substantially eliminates the need for many of the empirical adjustment factors currently required in the estimation of interface strength. The attachment includes a plurality of individual load cells configured in series, each of which measures the interface resistance due to the penetration of a sleeve with a selected surface texture into the soil. This configuration provides for multiple individual in situ measurements of interface strength at each measurement depth in a single sounding. The sleeves are interchangeable so that measurements corresponding to any desired roughness can be determined. In addition, with multiple fs values recorded at any given elevation within the same sounding, factors that affect fs can easily be determined since the lateral variability of the site is not an issue in the measurements.
In a preferred embodiment, the attachment module is configured with four individual load cells, each having a mandrel and a friction sleeve. Thus, the four load cells correspond to four multi-friction sleeve module measurements of interface strength. Additionally, in a preferred embodiment, the attachment module is configured with a conventional 15 cm2 CPT, allowing for simultaneous measurements of conventional CPT sensors (e.g. qc, u2, and fs ) in addition to the four multi-friction sleeve module measurements. Thus, the combined CPT module-attachment module system can provide seven individual in situ measurements of interface strength at each measurement depth in a single sounding.
In another embodiment, non-instrumented tips of varying lengths can be used with the penetrometer attachment in place of a conventional CPT module. Regardless of the specific configuration utilized, it is anticipated that the penetrometer attachment will enable direct in situ measurement of the relationship between surface roughness and hardness and interface strength.
These embodiments provide a method for determining in situ soil properties. In particular, a method is disclosed for direct, in situ measurement of the interface strength throughout the soil profile depth by determining the relationship between the interface strength and the hardness and surface roughness factors at desired measurement depths in a single sounding. In this regard, one embodiment of such a method, among others, can be broadly summarized by the following steps: collecting penetrating tip measurements; collecting attachment module measurements for each of said plurality of individual load cells, where said load cells are comprised of a corresponding plurality of friction sleeves; and transmitting said measurement data to a data acquisition system for manipulation and storage. This method may also include the steps of monitoring verticality, converting analog data to digital data, multiplexing data signals downhole, arranging a plurality of load cells in series, and configuring the attachment module for rapid set-up and easy modifications and configuring the friction sleeves with a diamond textured sleeve surface that is xe2x80x9cself-cleaningxe2x80x9d and capable of inducing shearing within the soil, instead of just along the interface.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.